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Jet_A_Knight
11th May 2003, 09:40
Looking at the nacelles on a B737 300/400/500 etc with the CFM56, the nacelles seem to have a profile similar to an aerofoil.

Maybe I should already know this, but does the shape generate some amount of lift in order to help support itself in flight (ie contibute to the a/c total lift with regard to generating some lift to account for it's own weight??)

PifPaf
11th May 2003, 09:52
Iīm not 100% sure, but the nacelles donīt contribute to generate lift.
Maybe you thougt this because the shape - it was made that way because the landing gear is too short, and the engines were too much near the ground. So, they decided to "round" the bottom!

PP

Mad (Flt) Scientist
11th May 2003, 13:45
Any minor effect of lift geenrated directly by the engine nacelles is unfortunately countered by the serious disturbance to the wing flow created by the nacelles and pylons. Engines mounted on the wing are generally a net decrement to the lifting capability of the aircraft (with the obvious exceptions of powered lift, both hjet and prop).

Furthermore, the main effort behind any nacelle shaping will be to provide the best possible conditions for engine operation; no other requirement is as important. It's simply not worth compromising on that one to generate a little bit of lift.

As an aside, a body doesn't have to be "aerofoil-shaped" to generate lift, of course. Underwing stores (e.g. fuel tanks) are longitudinally destabilising when projected forward of the leading edge because they generate lift. And aft-mounted engines act to stabilise the aircraft slightly, in the fashion of a very inefficient tailplane. But neither case is designed to do that.

Jet_A_Knight
11th May 2003, 20:20
Thanks.

I figured the shape of the bottom of the nacelle was due to stumpy ldg gear, but it was more the shape of the top of the nacelle that 'got me thinking'.

lomapaseo
11th May 2003, 21:41
Yes, the inlet part of the nacelle does contribute to lift by virtue of the air being passed into it . A vertical cross section of the nacelles, typically used on wing mounted engines cantilevered forward of the wing, is asymetric compared to its horizontal cross section.

used2flyboeing
23rd Jun 2003, 08:49
NACELLES CONTRIBUTE TO LIFT - THIS LIFT IS MEASURED DURING A WING DEVELOPMENT PROGRAMS IN WINDTUNNELS - THE AERODYNAMIC SHAPE OF THE 737 NECELLE IS NOTHING MORE THAN A FLAT ON THE BOTTOM FOR GROUND CLEARANCE - I BELIEVE THE 737 NG Clearance is something like 16 inches - not much for a crab manuever ! Nacelles are very expensive parts & lifiting nacelles are very complicating parts - IE if you want a nacelle to product lift - why not just add a bigger wing ? Lifting nacelles complicate the hell out of engine mounts etc. - therefore - it is not something being pursued because it is just easier to make a better wing & try to make the nacelle not hose up all that delightful development on the wing's aero - my 2 cents .. Lifitng nacelles have been explored - but the non symettrical shapes IE two halves of the nacelle are not the same - double the cost of manufacturing & sparing. Look at AIRBUS - both halves are interchangeable - IE cheaper to make & cheaper to spare - only need to keep one universal part instead of a left & right hand part ..